Chemistry Reference
In-Depth Information
Eqs (2.312) - (2.315):
petroleum
!
60
°
C
Ti
OPr
i
4
C 4LiR
TiR
4
C 4LiOPr
i
2
.
312
where R D l-adamantylmethyl.
970
VO
OPr
i
3
C ZnMe
2
! MeVO
OPr
i
2
C
4
[MeZnOPr
i
]
4
971
2
.
313
M
OPr
i
5
C 3LiR ! MR
3
OPr
i
2
C 3LiOPr
i
2
.
314
where M D Nb, Ta; R D Me, CH
2
Bu
t
.
972
Ta
OMe
5
C 4LiCH
2
SiMe
3
! Ta
OMe
CH
2
SiMe
3
4
C 4LiOMe
972
2
.
315
The alkylation of alkoxides of niobium and tantalum rarely lead to total substitution.
Typically the reaction is free from any complication and the products are pure up to
the trisubstitution stage.
In the reactions with Cr
OBu
t
4
, the solvent plays a determining role. For example,
reactions with methyllithium or Grignard reagents in the presence of donor solvents
(such as THF or diethyl ether) yield the corresponding
n
-bonded tris(organo)chromium
complex.
petroleum
!
78
°
C
Cr
OBu
t
4
C 4LiR
CrR
4
C 4LiOBu
t
2
.
316
where R D Me, Pr
i
,Bu
n
,Bu
i
,CH
2
Bu
t
,Bu
t
,
973
,
974
l-adamantylmethyl.
970
C8PhMgBr
! 2CrPh
3
thf
3
C Ph - Ph C 8Mg
OBu
t
Br
975
(2.317)
THF
C8EtMgBr
2Cr
OBu
t
4
! 2CrEt
3
thf
x
C 8Mg
OBu
t
Br C 2C
2
H
6
C C
2
H
4
975
THF
(2.318)
C8MeMgBr
! 2CrMe
3
thf
x
C 8Mg
OBu
t
Br C 2CH
4
(2.319)
THF
4.15 Tischtchenko, Meerwein-Ponndorf-Verley (M -P-V) and Oppenauer
Oxidation Reactions
4.15.1
Introduction
Metal alkoxides are known to act as potential catalysts (Chapter 7, Section 4) and this
property has been utilized successfully in organic syntheses. Before dealing with the
Tischtchenko, Meerwein - Ponndorf - Verley, and Oppenauer oxidation reactions, it is
worth briefly mentioning the Cannizzaro reaction which appears to be the main basis
